TX, you're on the right track, essentially. You need to open up the ceiling, have a look at where you can fit the skylight between the rafters, and what that means in terms of your ceiling (best case scenario is that rafters and ceiling joists are aligned, and you can just drop the light, build a box and call it done. If things aren't that well lined up, then you may have to get a bit creative.
Roofside, you usually need some kind of 90 degree flashing to tuck under the shingles, and under some kind of flange on the light. Don't spare the Tar. Roofs don't need to be pretty, they need to be dry.